The present invention relates to a digital convergence correction system used for convergence correction of the screen of a display unit including the color television receiver or a display terminal using a cathode ray tube (CRT), or more in particular to a method for preparing convergence correction data for the convergence correction system.
Generally, a digital convergence correction system is used for correcting the convergence by determining the correction amount for each position requiring convergence correction on the screen, storing the correction data in digital form in memory as a correction data, reading the correction data in synchronism with the CRT screen scanning, and converting the correction data into an analog signal at a D/A converter.
The conventional digital convergence correction system described above is disclosed, for example, in JP-A-56-169985. According to this conventional convergence correction system, the job of determining all the correction data for all positions requiring convergence correction on the screen is too burdensome and not practical, and therefore the method as mentioned below is employed.
Specifically, several adjusting points representative of positions requiring convergence correction are designated on the screen. The correction data for these adjusting points are obtained by actual adjusting work. The correction data for a given position (correction position) between adjusting points is prepared by an interpolating operation using the correction data for two vertically adjacent adjusting points on the opposite sides of the particular position. This interpolating operation is performed by a linear method using the difference between the correction data at vertically two adjacent points.
FIG. 2 is a diagram for explaining an example of reference pattern for adjustment displayed on the screen in order to set an adjusting point on the screen. In FIG. 2, adjusting points are set at the positions of lattice points of a cross-hatched pattern (lattice pattern). Normally, in order to secure an adjusting point at the center of the screen, an odd number of adjusting points are provided in both vertical and horizontal directions.
FIG. 3 is a diagram for explaining the case in which the correction data at a given position between two adjacent adjusting points on a line of lattice points (adjusting points) in FIG. 2 is determined by linear interpolating operation using the difference of correction data between the two adjusting points. FIG. 4 is a diagram showing a hypothetical case where ideal correction data is obtained not by a linear approximation, but by some method or other, for the sake of comparison. In these diagrams, white circles represent adjusting points, and character x designates the position of an adjusting point (scanning line number) and character y the correction data of an adjusting point.